\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(-40:1.5){A}
    \tkzDefPoint(20:1.5){B}
    \tkzDefPoint(50:1.5){C}
    \tkzDefPoint(51:1.5){D}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawSegments(O,A  O,B  O,C  O,D)
    \tkzMarkAngle[size=.6](A,O,B)
    \tkzDrawPoint(O)
    \tkzLabelPoints[left](O)
    \tkzLabelPoints[right](A,B)

    %
    \tkzDefPoint(-20:0.6){e1}  % End point
    \tkzDefPoint(-20:1.8){b1}  % Begin point
    \tkzDrawSegment[-latex](b1,e1)
    \tkzLabelSegment[pos=0, right](b1,e1){$n^\circ$圆心角}

    \tkzDefPoint(5:1.5){e2}
    \tkzDefPoint(5:1.8){b2}
    \tkzDrawSegment[-latex](b2,e2)
    \tkzLabelSegment[pos=0, right](b2,e2){$n^\circ$弧}

    \tkzDefPoint(50.5:1.2){e3}
    \tkzDefPoint(30:1.8){b3}
    \tkzDrawSegment[-latex](b3,e3)
    \tkzLabelSegment[pos=0, right](b3,e3){$1^\circ$圆心角}

    \tkzDefPoint(50.5:1.5){e4}
    \tkzDefPoint(45:1.8){b4}
    \tkzDrawSegment[-latex](b4,e4)
    \tkzLabelSegment[pos=0, right, yshift=.3em](b4,e4){$1^\circ$弧}
\end{tikzpicture}

